JEE Main & Advanced Mathematics Circle and System of Circles Question Bank System of circles

  • question_answer
    The locus of centre of a circle passing through (a, b) and cuts orthogonally to circle \[{{x}^{2}}+{{y}^{2}}={{p}^{2}}\], is                [IIT 1988; AIEEE 2005]

    A)            \[2ax+2by-({{a}^{2}}+{{b}^{2}}+{{p}^{2}})=0\]

    B)            \[2ax+2by-({{a}^{2}}-{{b}^{2}}+{{p}^{2}})=0\]

    C)            \[{{x}^{2}}+{{y}^{2}}-3ax-4by+({{a}^{2}}+{{b}^{2}}-{{p}^{2}})=0\]

    D)            \[{{x}^{2}}+{{y}^{2}}-2ax-3by+({{a}^{2}}-{{b}^{2}}-{{p}^{2}})=0\]

    Correct Answer: A

    Solution :

               Let equation of circle be \[{{x}^{2}}+{{y}^{2}}+2gx+2fy+c=0\] with \[{{x}^{2}}+{{y}^{2}}={{p}^{2}}\] cutting orthogonally, we get \[0+0=+c-{{p}^{2}}\]or \[c={{p}^{2}}\] and passes through (a, b), we get                    \[{{a}^{2}}+{{b}^{2}}+2ga+2fb+{{p}^{2}}=0\] or                    \[2ax+2by-({{a}^{2}}+{{b}^{2}}+{{p}^{2}})=0\]                    Required locus as centre \[(-g,\ -f)\] is changed to (x, y).


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